Radio receiving system



Feb. 8, 1938. K. SCHLESINGER RADIO RECEIVING SYSTEM 2 Sheets-Sheet 1Filed Dec. 13, 1934 RADIO RECEIVING SYSTEM Filed Dec: 13, 1954 2Sheets-Sheet 2 Fig.5-

Patented Feb. 8, 1938 UNITED STA? Application December 13, 1934, SerialNo. 757,360 in Germany December 13, 1933 7 Claims.

The invention relates to a back-coupling arrangement for a receiverwithout transposing the received frequency or with transposing thereceived frequency fe to a higher or lower inter 5 mediate frequency jzby means of a local oscil lation frequency i The connection systemsaccording to the invention possess the following essential advantages incomparison with the known connections:

1. A considerably increased degree of amplificaticn (reckoned as theratio between the intermediate frequency amplitude AZ and the receivingamplitude Ac),

2. An increased selectivity,

3. Elimination of the radiation of the local oscillation I According tothe invention the degree of amplification and selectivity is increasedby using back-coupling for the receiving frequency or for theintermediate-frequency and by extending this back-coupling to such adegree that normally self-excitation would take place. Thisself-excitation is prevented by causing the tube to oscillate with afrequency greater than the backcoupled frequency.

The principle according to the invention will be best explained inconjunction with the connection systems according to the annexed Figures1-4, in which exemplary embodiments of transposition connections areshown.

Fig. 1 shows a circuit diagram of a superheterodyne receiver accordingto the invention.

Fig. 2 shows a circuit diagram of a receiver without using transposingthe frequency.

'5 Fig. 3 shows a superheterodyne receiver with two mixing tubes inpush-pull connection and Fig. 4 shows a modification of the circuit ofFig. 3.

In particular with reference to Fig. 1 a local oscillator l withscreening grid, and preferably with twin control grids 2 and 3, is inself-excitation with the natural wave of the circuit 4, 5, and thusproduces the frequency ,ffi- The superimposed connection is built up ascapacitative or inductive three-point connection, whereby thecapacitative connection is preferably employed for short to ultra-shortwaves, and the inductive connection for long waves. At a centre-tappedpoint 6 of this local oscillation circuit there is coupled theintermediate frequency circuit 7, 8. The feeding of this circuit withthe anode potential or the dynamic earthing of this circuit through themedium of the blocking condenser 9 also takes place in a centre-tappedpoint of the sc circuit,

The operation of the exemplary embodiment of an arrangement according tothe invention may be clearly understood by the following explanationswith respect to Fig. 1. The input circuit i5, i5 is tuned to thefrequency value of the oscillations to be received and leads viacondenser iii to one grid (2) of the mixing stage i, said grid (2) beingsupplied with a suitable bias via the resistance-arrangement IT, IS. Theother grid (3) of said mixing stage i is connected by means of thecoupling-condenser .H and the oscillatory circuit i, 5 with the anode ofvalve i. This oscillatory circuit is tuned to a very high frequency ffi,which represents the superheterodyne frequency.

In view of the inherent capacities of the valve l between the grids 2and 3 and the anode of said valve the circuit generates the frequency iand simultaneously the input grid 2 controls the electron stream ofvalve 2, such producing in the of coil 5 and earth, said circuit 1, 8having a U centre tap of its coil earthed by means of a condenser 9. Inorder to obtain a large amplication degree for the desired intermediatefrequency z a bacl -coup-1ing is used between the oscillatory grid andcircuit and the anode circuit for the intermediate frequency by means ofcondenser lil. This back-coupling effect may be increased in such amanner that, normally, if the oscillatory circuit i, 5 would not existin the anode circuit, a self-oscillating effect with respect to theintermediate frequency would arise. Since in this case of self-oscillating in the frequency jz this frequency fz could not be furtherused in the associated circuit, this self-oscillating of theintermediate frequency z must be prevented which is realized by the useof the oscillatory circuit tuned at a frequency value much greater thanthat of fz. It is known to persons of ordinary skill in the art that inview of the self-oscillating effect of the valve in the frequency ffihaving a greater value than that of the frequency fz a self-oscillatingof the oscillation having the frequency fz is prevented. In view of thiseffect it is possible to make the degree of the back-coupling extremelyhigh, 1. e. these circuits are firmly The anode circuit of said mixing lcoupled, such producing a high amplification for the amplitudes of theintermediate frequency fz which is most important for the efficiency ofthe circuit arrangement, such high degree of backcoupling beingimpossible in normal circuits without using the circuit 4, tuned to afrequency higher than the desired frequency to be used in the associatedstages.

The centre-tapped connections are required for the feed-supply of theanode of valve l for preventing detrimental efi'ects upon the resonantcircuits by unsymmetrical conditions.

The circuit 1, 8 is coupled inductively with a band-filter outputcircuit I3, [4, which is also tuned to the frequency fz. Theamplification of the mixing stage I may be additionally regulatedwithout interruption of the oscillations by means of a potentiometer I!connected with the negative pole of the anode current source through themedium of a grid resistance 18 in place of which, as well known, theremay also be employed an automatic regulating means.

The condenser may be used for neutralizing the currents of theoscillatory frequency ffl coupled by the inherent capacities of thevalve to the input-grid circuit, such preventing radiating of the localoscillations by the aerial.

The considerable improvement in the efficiency of a connection systemaccording to the invention asserts itself in comparison with the knownconnections principallybecause the intermediate frequency circuits inthe usual combined detector oscillator circuits are, owing to thepresence of very powerful amplitude in the connected mixing tubes,always loaded by extensive auxiliary damping from the tube, which mayalso be compensated by the method of back-coupling arrangement accordingto the invention.

Elimination of the radiation of fii from the aerial is accomplished inaccordance with the invention by a condenser 20, which compensates thecomponent potential of Afi transmitted by the internal capacity 2|between the twin grids by a counter-phasic coupling from the anode.

The invention may also be employed as sensitive, back-coupled singlecircuit receiver without utilizing a frequency transposition. For thispurpose with reference to Fig. 2 the circuit 15, I6 coupled with theaerial and also circuit 1, 8 shown in Fig. 1 is tuned to the receivingfrequency. The short-wave oscillation circuit 4, 5 is tuned to a wavewhich is shorter than any wave which may be received. Short waveoscillations generated by the circuit 4, 5 prevent in accordance withthe invention the self-excitation of the receiving frequency, and'thereis obtained at the circuit 1, 8 a considerable selectivity andhigh-frequency amplification without cause for anxiety that this circuitmight undergo self-oscillation. It is possible to transmit the amplifiedreceiving-high frequency to a circuit 1a, 8a, coupled with the circuit1, 8 and to rectify in a separate tube connectecl with the circuit Ia,8a, or rectification may be performed in the same tube by means ofaudion connection shown in Fig. 2 or by means of the twin gridconnection 2 shown in Fig. 1. A special manipulation regulation of thebackcoupling between the circuits l5, l6 and I, 8 is unnecessary in thecircuit according to the invention even upon variation of the receivedwave, which represents a considerable improvement as compared with theknown back-coupling connections without a short auxiliary wave.

When using a twin-grid tube shown in Fig. 1 the control efficiency foreach control grid is halved because each of both control grids is passedonly by one half of the electronic stream. According to an additionalfeature of the invention, it is possible to operate with full control'efficiency by using circuits with two tubes in pushpull connectionsshown in Figs. 3 and 4. The

desired intermediate frequency potential A; is tapped as the differencepotential of the anodes of the two mixing tubes in relation to eachother. The input receiving potential is passed to each grid incounter-phase if the superposition on both grids is co-phasal or ifnecessary reversed. The first method is employed according to Fig. 3primarily in the case of infradyne connections, in which theintermediate frequency fz to be obtained is in the order of the localoscillation I and the latter on the other hand in superheterodynereceiver connections, in which fz is much longer than ffi.

Fig. 3 shows two mixing example twin-grid tubes. Single-grid tubes,however, are also suitable, and these may then have twice the steepness.The anodes of these tubes are connected through the medium of anintermediate frequency circuit comprisingthe tubes Hand 23, for

condenser 24, the coil 25, and the differential.

capacity 26 forming apart'of the oscillatory circuit capacity. Theself-excitation of the tubes takes place through the oscillatory circuit21, 28

in equal cadence for both grids. For this purpose the coil 28 is tappedat the centre, or the-condenser 21 earthed at the centre (differentialcondenser). The feeding of this local oscillation f occurs in each casethrough a part-plate 29 or 30 of a differential condenser. Theadditional back-coupling for the intermediate frequency in accordancewith the invention may be established and regulated through the mediumof another plate-armature 3| or 32 of the same differential condenser byconnection in each case with the anodes of the other tube. Theoscillatory grids are leaked off over resistances 33, 34, whereby a verydesirable negative charging of the same is capable of being adjusted.The reception is fed in counter-cadence from the aerial circuit 4| overthe circuit 35, 36, whereby this circuit is earthed at the centrethrough the medium of a condenser 31, and a regulable negative grid biaspassed to the same through the medium of a series resistance 38. anodepotential takes place at the centre of the intermediate circuit coil 25.This supply circuit damps the local oscillation frequency ffi producedin cadence, and must, therefore, be supplied through the medium of aresistance 39, which is large for this frequency. For this purpose theremay also be employed the part windings of the choke 25. The connectionsystem has the advantage of a complete de-coupling of the intermediatefrequency circuit from the local oscillation circuit even in the case ofslight difference in frequency between the same. A band filter outputcircuit 40 is coupled with the circuit 24, 25. In the circuit 40 theinduced E. M. F. is proportional to the input receiving potential anddisappears if the input receiving potential in the circuit 35,36disappears. Beyond this the aerial 4| coupled with the circuit 35, 36 isin each The feeding of the tube with the case free of radiation ascompared with the,

ficient amount at the anodes.

=-additional back-coupling of the so that its full potential reaches thegrids of these tubes. The tubes are in counter-cadence self-excitationon the local oscillation frequency i of the circuit 46, 41. Theelectrical centre of 46, 4'! is found by a differential condenser 48, sothat the connection is again free of radiation against the localoscillation. If twin grids 49, 50 are provided, this differentialcondenser may be omitted and wiring performed as shown in broken lines.Automatic or manually operated volume control may then be introducedproceeding from a counter-potential Otherwise this bias should beapplied in common to the grids shown in solid lines. The self-excitationtakes place through the medium of two small condensers 52, 53(approximately cm.), for example Mesny condensers. Two oscillatorychokes 54, 55 ensure that potentials of the high local oscillationfrequency are able to build up in suf- They allow, however, thelong-Wave intermediate frequency-fa to reach the circuit 56, 51 withoutbeing weakened. Two larger condensers 58, 59 (approximately 50 cm.) maythen be employed for the intermediate frequency fiz according to theinvention. Its simultaneous superposition to the already existing gridpotentials of the frequency in takes place in the form of embodimentaccording to Fig. 3 by capacitative distribution of potential,

whereby the small condensers 60, Bl (approximately 10 cm.) ensure thatthe back-coupled intermediate frequency potential is not possiblyshort-circuited by the local oscillation circuit ii, 45. The samepurpose is served by the series resistances 62, 53 of approximately 1000ohms, which cause the local oscillation frequency c not to be possiblyinterrupted upon the application of the intermediate frequencyback-coupling 58, 59 owing to short-circuiting of the oscillatory chokes54, 55. Naturally the same result may also be obtained by methods knownper se of mixing two greatly diifering frequencies. In place of thecapacitative back-coupling it is also readily possible to employ aninductive backcoupling, and in place of the stated parallel feed of thetwo oscillatory grids there may also readily be employed a seriesfeeding of the same. A band filter 64, 65 is coupled with theintermediate frequency circuit 56, 51, and allows the intermediatefrequency to be tapped without interfering traces of local oscillationfrequency.

According to the invention, the fading regulation may extend not only tothe twin grids 49, 50 but at the same time also to the oscillator grids,as in the stated connection the beginning of the generation of theoscillations is very soft, more particularly when using audioncombination with highly ohmic resistances 66, 61. An additionaladvantage of this connection system is the elimination of certainharmonics of the superposition and the reception, and accordingly areduction in the number of the usual whistling points in thesuperheterodyne receiver. The feeding with anode current does not dampany of the existing oscillations with the exception of the receivedwave, which is amplified directly in cadence, this being in any casedesirable. The blocking condenser 68 causes a dynamic earthing of thecircuit middle point of fz.

In the case of all connections referred to the possibility is providedfundamentally of adjusting the selectivity of a heterodyne receiver byhand by a special adjustment knob (the backcoupling passage of [2). Thesimultaneously increasing amplification may in accordance with theinvention be kept down by means of a sound-regulating device in theapparatus. A

receiving apparatus is accordingly provided, the selectivity of whichmay be adjusted by hand according to requirements in individual cases.In the case of a close coupled band filter cascade as hitherto usualthese possibilities do not exist. In face of these connections themethod according to the invention possesses the additional advantage ofa great decrease in the number of circuits. methods of eliminating lossby back-coupling, the method according to the invention offers theconsiderable advantage that even in the case of exaggeratedback-coupling a self-excitation of the oscillatory circuit free ofattenuation is unable to occur, as this is always withheld by the localoscillation.

I claim:

1. In a radio-receiver an'electronic valve hav ing a cathode, an anodeand at least two controlgrids, a receiving input circuit coupledwith anaerial circuit and connected with said cathode and one of said controlgrids, an oscillatory circult tuned to a frequency greater than thereceiving frequencies and connected with said anode and the other ofsaid control grids, a back-coupling circuit for the receiving frequencyconnected with a tapped-point of said oscillatory circuit and an anodecurrent source and firmly coupled with said receiving input circuit.

2. In a superheterodyne receiver an electronic valve having a cathode,an anode and at least two control-grids, a receiving input circuitcoup-led with an aerial circuit and connected with said cathode and oneof said control-grids, an oscilla tory circuit for producing aninterinedate frequency connected with said anode and the other of saidcontrol-grids, an intermediate frequency circuit connected with atapped-point of said oscillatory circuit, a back-coupling circuit forsaid intermediate frequency, said oscillatory circuit tuned to'afrequency greater than the intermediate frequency, therefore generatingoscillations preventing self-excitation for the intermediate frequency.

3. In a superheterodyne receiver an electronic valve having a cathode,an anode and at least two control-grids, a receiving input circuitcoupled with an aerial circuit and connected with said cathode and oneof said control grids, an oscillatory circuit for producing anintermediate frequency connected with said anode and the other of saidcontrol-grids over a block-condenser, an intermediate frequency-circuitconnected with a tapped-point of said oscillatory circuit and over avariable condenser with said second control grid and over a resistancewith said cathode, therefore effecting a back-coupling for theintermediate frequency, a tapped-point of said intermediate frequencycircuit connected over a resistance with an anode-current source andover a condenser with an earthing point, said oscillatory circuit tunedto a frequency greater than the intermediate frequency, thereforegenerating oscillations preventing self-excitation for the intermediatefrequency.

4. In a superheterodyne receiver an electronic valve having a cathode,an anode, and. at least two control-grids, a receiving input circuitcoupled with an aerial circuit and connected with said cathode and oneof said control-grids, an oscillatory circuit for producing anintermediate frequency connected with said anode and the As comparedwith the known other of said control-grids over a block-condenser, anintermediate frequency-circuit connected with a tapped-point of saidoscillatory circuit and over a variable condenser with said secondcontrol grid and over a resistance with said cathode, thereforeeffecting a back coupling for the intermediate frequency, a tapped-pointof said intermediate frequency connected over a resistance with ananode-current source and over a condenser with an earthing point, saidoscillatory circuit tuned to a frequency greater than the intermediatefrequency, therefore generating oscillations preventing self-excitationfor the intermediate frequency, said intermediate frequency circuitbeing coupled with a band-filter output circuit.

5. In a superheterodyne receiver an electronic valve having a cathode,an anode and at least two control-grids, a receiving input circuitcoupled with an aerial circuit and connected with said cathode and oneof said control grids, an oscillatory circuit for producing anintermediate frequency connected with said anode and the other of saidcontrol-grids over a block-condenser, an intermediate frequency-circuitconnected with a tapped-point of said oscillatory circuit and over avariable condenser with said second control grid and over a resistancewith said cathode, therefore effecting a backcoupling for theintermediate frequency, a tapped-point of said intermediate frequencyconnected over a resistance with an anode-current source and,

over a condenser with an earthing point,v said oscillatory circuit tunedto a frequencygreater than the intermediate frequency, thereforegenerating oscillations preventing self-excitation for the intermediatefrequency, said intermediate frequency circuit being coupled with abandfilter output circuit, the internal capacity between saidcontrol-grids being compensated by a neutrodyne condenser.

6. In a superheterodyne receiver two electronic valves, each of whichhaving a cathode, an anode and at least two control grids, a receivinginput circuit coupled with anaerial circuit and connected with thecontrol grids of said valves, the control grids of said valves connectedover differential condensers with each other, with the one side of anoscillatory circuit for producing an intermediate frequency and with anintermediate frequency circuit, the other side of oscillationspreventing self-excitation for the in-v termediate frequency.

In a superheterodyne receiver two electronic valves each of which havinga cathode, an anode and at least two control grids, one control grid ofone of said valves connectedrwith one control-grid of the otherof saidvalves and with a receiving input circuit coupledwith an aerial circuit,the other control grids of said valves connected over block-condenserswith an oscillatory circuit and over small condensers with an anode ofthe other valve, an intermediate frequency circuit connected overoscillating coils with the anode of said valves, a tapped point of saidintermediate frequency circuit connected with an anode current source,the cathodes of said valves connected with each other,

with the earthing point, with the mid-point of said oscillatory circuitand over a condenser with the mid-point of said receiving input circuit,said osciliatory circuit tuned to a frequency greater than theintermediate frequency therefore generating oscillations preventingself-excitation for the intermediate frequency.

KURT SCHLESINGER.

